A 3 g sample of air dried soil is shaken with 30 mL of Mehlich III extracting solution [0.2 N CH3COOH, 0.25 N NH4NO3, 0.015 N NH4F, 0.013 N HNO3, and 0.001 NEDTA] for 5 min. and then centrifuged. The supernatant is analyzed for Ca, Cu, K, Mg, Mn, P, and Zn by ICP-AES.
(See Method References No. 34 & 21)